// 基于下面提供的代码，完成后续的四个练习
class Container {
  static of(value) {
    return new Container(value)
  }
  constructor(value) {
    this._value = value
  }
  map(fn) {
    return Container.of(fn(this._value))
  }
}
class Maybe {
  static of(value) {
    return new Maybe(value)
  }
  isNothing() {
    return this._value === null || this._value === undefined
  }
  constructor(value) {
    this._value = value
  }
  map(fn) {
    return this.isNothing() ? this : Maybe.of(fn(this._value))
  }
}
module.exports = { Maybe, Container }

// 练习1：使用fp.add(x, y)和fp.map(f, x)创建一个能让functor里的值增加的函数ex1
const fp = require('lodash/fp')
const { Maybe, Container } = require('./support')
let maybe = Maybe.of([5, 6, 1])
let ex1 = () => {
    return maybe.map(fp.map(a => fp.add(a, x)))
}

//  实现一个函数ex2 ,能使用fp.first获取列表的第一个元素

const fp = require('lodash/fp')
const { Maybe, Container } = require('./support')
let xs = Container.of(['do', 'ray', 'me', 'fa', 'so', 'la', 'ti', 'do'])
let ex2 = () => {
  return xs.map(fp.first)
}

// 实现一个函数ex3，使用safeProp和fp.first找到user的名字的首字母。
const fp = require('lodash/fp')
const { Maybe, Container } = require('./support')
let safeProp = fp.curry(function(x, o) {
  return Maybe.of(o[x])
})
let user = { id: 2, name: 'Albert' }
let ex3 = () => {
    // todo
    let safe = safeProp('name',user)
    let names = safe.map(name=>name.split('')).map(fp.first)
    return names
}

// 练习4：使用Maybe重写ex4，不要有if语句
const fp = require('lodash/fp')
const { Maybe, Container } = require('./support')
let ex4 = function(n) {
  return Maybe.of(n).map(parseInt)
}
